Concrete is a composite material made by mixing cement, aggregate such as sand or gravel, and water. It is strong in compression but requires steel reinforcement to handle tensile and shear stresses. There are different types of cement used for concrete depending on the application, and concrete can be formed into various shapes and textures. Reinforcing steel such as rebar or welded wire fabric is embedded in concrete to improve its tensile strength and durability. The water-cement ratio, workability, and compressive strength of concrete are tested through procedures like the slump test and compression test.

1. Materials & Construction-I (AR-112)
Resource Persons:
Farah Jamil & Amir Jamal
Department of Architecture
University of Management and Technology, Lahore
2. Concrete

2. Concrete
 Concrete is made by mixing:
1. Cement.
2. Mineral aggregates.
3. Water.
 Concrete is inherently strong in
compression, steel reinforcement is
required to handle tensile and shear
stresses.

3. Concrete
 Concrete is capable of being formed into
almost any shape with a variety of
surface finishes and textures.
 Concrete structures are relatively low in
cost and fire-resistant.

4. Cement
Portland cement is a hydraulic cement
made by burning a mixture of clay and
limestone in a rotary kiln and pulverizing
the resulting clinker into a very fine powder.

5. Types of Cement
 Type I - Normal
Portland Cement is
used for general
construction, having
none of the
distinguishing qualities
of the other types.

6. Types of Cement
 Type II - Moderate
Portland Cement is
used in general
construction where
resistance to moderate
sulfate action is required
or where heat buildup
can be damaging, as in
the construction of large
piers and heavy retaining
walls.

7. Types of Cement
 Type III - High-early-strength portland
cement cures faster and gains strength
earlier than normal Portland cement.
 It is used when the early removal of
formwork is desired, or in cold-weather
construction to reduce the time required
for protection from low temperatures.

8. Types of Cement
 Type IV - Low-heat Portland Cement
generates less heat of hydration than
normal Portland cement.
 It is used in the construction of massive
concrete structures, as in gravity dams,
where a large buildup in heat can be
damaging.

9. Types of Cement
 Type V - Sulfate-Resisting Portland
Cement is used where resistance to
severe sulfate action is required.
 It is designated by the suffix ‘SR’.

10. Types of Cement
 Air-Entraining Portland Cement is a
Type I, Type II, or Type III Portland
cement to which a small quantity of an
air-entraining agent has been
interground during manufacture.
 It is designated by the suffix ‘A’.

12. Water
 The water used in a concrete mix must
be free of organic material, clay, and
salts.
 A general criterion is that the water
should be fit for drinking.
 Cement paste is a mixture of cement
and water for coating, setting, and
binding the aggregate particles together
in a concrete mix.

13. Aggregate
 Aggregate
refers to any
inert mineral
materials, as
sand and
gravel, added to
a cement paste
to make
concrete.

14. Aggregate
 Aggregate represents from 60% to 80%
of the concrete volume, its properties are
important to the strength, weight, and
fire-resistance of the hardened concrete.

15. Aggregate
 Aggregate should be:
1. Hard.
2. Dimensionally stable
3. Free of clay, silt, and organic matter
that can prevent the cement matrix
from binding the particles together.

16. Types of Aggregate
 Fine aggregate consists of sand having
a particle size smaller than 1/4" (6).
 Coarse aggregate consists of crushed
stone, gravel, or blast-furnace slag
having a particle size larger than 1/4" (6).
 The maximum size of coarse aggregate
in reinforced concrete is limited by the
size of the section and the spacing of
the reinforcing bars.

17. Concrete Types
Structural lightweight concrete
 Is made with expanded shale or slate
aggregate
 Has a unit weight from 85 to 115 pcf
and compressive strength comparable
to that of normal concrete.

18. Concrete Types
Insulating Concrete
 It is made with
perlite aggregate
or a foaming
agent.
 It has a unit weight
of less than 60 pcf
(960 kg/ m3) and
low thermal
conductivity.

19. Concrete Admixtures
 Admixtures may be added to a
concrete mix to alter its properties or
those of the hardened product.
1. Air-entraining agents.
2. Accelerators.
3. Surfactants.
4. Superplasticizers.
5. Coloring agents.

20. Concrete Admixtures
1. Air-entraining agents disperse
microscopic, spherical air bubbles in a
concrete mix to increase workability,
improve resistance of the cured product to
the cracking induced by free-thaw cycles
or the scaling caused by deicing
chemicals, and in larger amounts, to
produce lightweight, insulating concrete.

21. Concrete Admixtures
2. Accelerators hasten the setting and
strength development of a concrete mix,
while retarders slow the setting of a
concrete mix in order to allow more time
for placing and working the mix.

22. Concrete Admixtures
3. Surface-active agents, or
surfactants, reduce the surface tension
of the mixing water in a concrete mix,
thereby facilitating the wetting and
penetrating action of the water or aiding in
the emulsifying and dispersion of other
additives in the mix.

23. Concrete Admixtures
4. Water-reducing
agents, or
Superplasticizers,
reduce the amount of
mixing water required for
the desired workability of
a concrete or mortar mix.
Lowering the water-
cement ratio in this
manner generally results
in increased strength.

24. Concrete Admixtures
5. Coloring agents are pigments or dyes
added to a concrete mix to alter or control
its color.

25. Water-Cement Ratio
Water-cement ratio is the ratio of mixing
water to cement in a unit volume of a
concrete mix, expressed by weight as a
decimal fraction or as gallons of water per
sack of cement.

26. Water-Cement Ratio
 It controls the strength, durability, and
watertightness of hardened concrete.
 According to Abrams’ law, formulated
by D. A. Abrams in 1919, the
compressive strength of concrete is
inversely proportional to the ratio of
water to cement.

27. Water-Cement Ratio
 If too much water is used, the concrete
mix will be weak and porous after
curing.
 If less water is used, the mix will be
dense but difficult to place and work.
 For most applications, the water-
cement ratio should range from 0.45 to
0.60.

28. Slump Test
Concrete is normally specified according to
the compressive strength it will develop
within 28 days after placement (7 days for
high-early-strength concrete).

29. Slump Test
Slump test is a method for determining
the consistency and workability of
freshly mixed concrete by measuring the
slump of a test specimen.

30. Slump Test
 It is expressed as the vertical settling,
in inches, of a specimen after it has
been placed in a slump cone, tamped
in a prescribed manner, and the cone is
lifted.

31. Compression Test
To determine the
compressive strength of
a concrete batch uses a
hydraulic press to
measure the maximum
load a test cylinder 6"
(150) ø and 12" (305)
high can support in axial
compression before
fracturing.

32. Steel Reinforcement
 Reinforcing bars are steel sections hot-
rolled with ribs or other deformations for
better mechanical bonding to concrete.

33. Steel Reinforcement
 The bar number
refers to its diameter
in eighths of an
inch—for example, a
#5 bar is 5/8" (16) in
diameter.

34. Steel Reinforcement
 Welded wire fabric consists of a grid of
steel wires or bars welded together at
all points of intersection.

35. Steel Reinforcement
 The fabric is typically used to provide
temperature reinforcement for slabs but
heavier gauges can also be used to
reinforce concrete walls.

36. Steel Reinforcement
The fabric is designated by the size of the
grid in inches followed by a number
indicating the wire gauge or cross-sectional
area.

37. Steel Reinforcement

38. Steel Reinforcement
 Reinforcing steel must be protected by
the surrounding concrete against
corrosion and fire.

39. Steel Reinforcement

40. Steel Reinforcement
Minimum requirements for cover and
spacing are specified by the American
Concrete Institute (ACI) Building Code
Requirements for Reinforced Concrete,
according to concrete’s exposure, and size
of coarse aggregate and steel used.